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In a gravimetric determination of P, an ...

In a gravimetric determination of `P`, an aqueous solution of dihydrogen phosphate ion `[H_(2)PO_(4)^(-)]` is treated with a mixture of ammonium and magnesium ions to precipitate magnesium ammonium phosphate, `[Mg(NH_(4))PO_(4).6H_(2)O]`. This is heated and decomposed to magnesium pyrophosphate `[Mg_(2)P_(2)O_(7)]`, which is weighed. A solution of `H_(2)PO_(4)^(-)` yielded `1.054 g of Mg_(2)P_(2)O_(7)`. What weight of `NaH_(2)PO_(4)` was present originally? `(Na=23, H=1, P= 31, O=16,Mg=24)`

Text Solution

Verified by Experts

`NaH_(2)PO_(4) rarr Mg_(2)P_(2)O_(7)`
apply POAC on P
Let wt of `NaH_(2)PO_(4)=w` gm
moles of P in `NaH_(2)PO_(4)=` moles of P in `Mg_(2)P_(2)O_(7)`
`w/120 times 1=1.054/232 times 2`
`w=1.054 times 120/232 times 2=1.09 gm`
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